The Catalan fish stew called suquet de peix traditionally is cooked in a cazuela, a wide, shallow terracotta dish, but a 12-inch skillet is a great alternative and what we use in this recipe. A combination of shrimp, mussels and flaky white fish in a saffron-scented tomato broth yields a dish full of color, shapes and texture. In the Catalan kitchen, picada refers to a mixture of nuts, garlic, bread and, often, other aromatic ingredients—from herbs to chilies, and even cooked chicken livers—pounded or ground to a thick paste. It’s used to add flavor to dishes of all sorts, or stirred into stews at the end of cooking to enrich and thicken the broth. We make a simple picada and hand-chop the ingredients, though you could bash the ingredients in a mortar with a pestle. Serve directly from the skillet, with warm, crusty bread for soaking up the broth.